Transcatheter valve implantation (for example, transcatheter aortic valve implantation (TAVI)) is an evolving technology for replacement valve therapy that (i) avoids the trauma of conventional open-chest surgery, and (ii) avoids the need for heart and lung bypass. In such a technique, a stent-valve is compressed and loaded into a delivery catheter. The delivery catheter is introduced to the desired site of implantation (for example at the heart) via a percutaneous route or via minimally invasive surgery. The stent-valve is expanded into the implantation position from or by the delivery catheter, and the delivery catheter is then withdrawn.
Despite the successes of transcatheter stent-valves, technological challenges remain. One such challenge is preventing retrograde leakage of blood around the stent-valve (so called para-valve leakage). The above-noted stents form a friction fit with the native anatomy to anchor the stent-valve in position, and are round in cross-section. However the native anatomy in which the stent is implanted is often off-round and is different for each person. Moreover, heavy calcification of the native anatomy may obstruct full deployment of any stent and make the native anatomy even more irregular. Thus, it can sometimes be difficult to provide a perfectly sealing fit between the stent-valve and the surrounding anatomy. Para-valve leakage is believed to be one of the factors affecting the long-term efficacy of the prosthetic valve, and possibly the life expectancy of the patient. One explanation is that the heart may have to work harder to compensate for some blood leaking retrograde at the entrance or exit of the heart. Therefore, addressing para-valve leakage is a significant challenge.
It is known to incorporate an external skirt or cover as part of the stent-valve. For example, the skirt is made of compressible biocompatible material, such as pericardial tissue or PET. The thicker the material of the skirt, the more able the skirt is to occlude gaps and effect a seal. However, a disadvantage is that such skirts add to the bulk of the stent-valve. A thick skirt makes the stent-valve problematic to compress to a desirably small size for implantation.
US-A-2005/0137688 is understood to describe compliant sacs disposed around the exterior of a stent, that are said to provide a more efficient seal along an irregular interface. The sacs may be filled with an appropriate material, for example, water, blood, foam or a hydrogel. Different arrangements of sacs are proposed in principle, but this document neither describes any specific construction technique nor does it describe handling of the fill material.
U.S. Pat. No. 5,769,882 is understood to describe an implantable expansible tubular vascular prosthesis carrying a form-in-place sealing layer for occluding at least a circumferential band at the interface between the prosthesis and the native tissue wall. In one example, the sealing layer comprises a hydrogel, arranged in a sleeve/cuff comprising a permeable membrane.
EP 1262201 is understood to describe an implantable vascular device having an external seal structure comprising a swellable hydrodel. In use, the hydrogel absorbs a mass of liquid so as to assume, as a result of the absorption, a certain degree of mechanical consistency. An example hydrogel has a polyvinyl alcohol (PVA) base, in combination with a polysaccharide.
WO-A-2008/070442 is understood to describe prosthetic heart valves, both expanding and non-expanding types, each having an anchoring sleeve that changes shape when the valve is implanted, to prevent migration of the valve. The anchoring sleeve is at least partly made of a material that swells due to absorption of body fluids. In examples, the sleeve is made of an inner material that swells upon contact with body fluids, and enclosed by a cover.
US-A-2007/0060998 and WO-A-2010/083558 are understood to describe delivery of a dispensable or releasable reactive sealing agent for endoluminal use around (at least substantially around) a prosthetic device within a body lumen. The reactive sealing agent is released or dispensed into a space between the prosthetic device and the lumen wall, in response to exertion of a dispensing pressure or by a configuration change causing the release. While different arrangements of dispensing capsules are proposed, reliable containment of the agent when the prosthesis is implanted at the heart likely are not ensured, especially in view of the constant movement and cyclic compression experienced by heart valves.
Accordingly, it would be desirable to address one or more of the above issues and/or provide a technique for mitigating para-valve (or para-stent) leakage without substantially affecting other desirable characteristics.